This invention relates to cathode ray tubes (CRTs) for color television, and more particularly relates to an internal contactor for electrically interconnecting the internal magnetic shield (IMS) and the anode coating on the inside surface of the funnel portion of the glass envelope of the CRT.
Cathode ray tubes (CRTs) for color television commonly incorporate a bowl-shaped internal magnetic shield (IMS), whose rim is attached to the rear of the frame supporting the aperture mask, and whose side walls extend rearward in proximity with the inside surface of the inwardly curving walls of the funnel-shaped glass envelope, and whose bottom wall defines a central aperture for passage of the electron beams to the aperture mask from the electron gun in the neck of the envelope.
The function of the IMS is to shield the electron beams from the earth's magnetic field, which field would otherwise cause the beams to deviate from their desired path through the apertures in the mask to the correct phosphor elements on the cathodoluminescent display screen on the inside surface of the face panel portion of the envelope.
In order to provide an equipotential electrical field for the beams' passage from the anode of the electron gun to the display screen, an evaporated aluminum layer on the screen is interconnected with the anode of the gun via the mask-frame-IMS assembly and a conductive coating on the inside surface of the envelope (termed herein the "anode coating"). The mask-frame-IMS assembly is commonly connected to the anode coating via one or more spring contactors extending from the IMS to the anode coating.
Various means have been employed to secure the spring contactor to the IMS, such as mechanical snap, clip or dart-clip arrangements. See for example, U.S. Pat. Nos. 3,541,373; 4,310,779; 4,333,033; 4,433,267; 4,670,686; and GB patent 2,236,897A. A common problem of these arrangements is that they tend to be less secure than joining the contactor to the IMS, such as by welding, and some, such as the dart-clip contactor of GB patent 2,236,897A, are difficult to manufacture.
However, welding also has drawbacks, including the generation of loose particles during welding. While most of these loose particles can be removed by washing, some of the wash water may be trapped in the small space between the IMS and the welded base of the contactor. This trapped water can corrode the weld, as well as other metal parts inside the CRT, and can also degrade the anode coating.